Cable fault locator



Oct. 6, 1959 R. A. ROGERS ET AL CABLE FAULT LOCATOR Filed Oct. 21, 1955Fis. 4.

f/vvEwToRs ROBERT A. ROGERS HERBERT V.JOHN5ON RUSSELL E. ROWE LL BATTORNEY 9 2,907,949 Patented. Cot.- 1959 2,907,949, 'GABLE F ULT-Locumo e t Aime b rt ohnson, nd; s e l Roiw l, F101 u e ale,

Application Gotcha 215 1955, senarN 5451,952- 7 1 laim. (Cl. 2 7 1 Thisinvention relates to cable fault locators particularly toa devicewhereby to quickly and easily locate the fault where the cablehas-become broken'or otherwise lnz hed aw a Figure- 1 isa sideelevation'of a, device constructed; in accordance with, the; invention,

F-igurezis a; side elevation thereof,

Figure 3 is atop pLan view ofthe device and, V

Figure; 4 is, aqdiagrarnmatie illustration of the instrw mentalitiesforindicating the presence of;eurrent leakage frornapable.

Rof m nst ao i o llyo the d aw gs. h s cm.- odiospair o p o d- -n z n Pra e ub la tati r 5;. conne t d t heir pper nd by.- l.- I! Q-- 6 t ouhe; medium o oh. e dev e s a ipu t eovvor dsf the standard are is y-oonno e y os ow heor s -hoad po si w r i e o gitu n sro odt a u o theadios-t b e econ io o ap r ppo i e y e t nd -n a d a ly tion in order tolocate the exact: point of' break within the cable.

'Fhe new design of fault locatorto bedescribed in this application isthe answer to thisproblem. The principle of this locator 'is measuringthe voltage drop across a resistance as the current through theresistance changes. In

this case the resistance is the earth and the current: is .that in the;street light circuit. when a faultgor ground occurs-on anundengroundseries street light cable; (directburial nonmetallic sheath cable), theeurren-n fiunnished by the; onstant-current street light transformer;will/enter into the; earth surrounding the cable Will Seek a-ipfifhthrough the earth to anybtherpointon the circuit that is grounded. Thestreet lights between these two grounds Will; be out; or, burning dimdepending.- on the deg-rec of fault on the cable. The fault current willbe greatest at the point where it leaves the cable and enters the earth.By probing the ground above the cable with this fault locator, the exactspot where the fault exists will be indicated. The indicator in thisdevice is a 0-50 micro ampere direct-current microammeter. In as much asthe street light circuit is alternating current, a rectifier is neededto operate the direct-current meter. A O100,000 ohm potentiometeroperates as a sensitivity control to keep the needle of the meter onscale.

The purpose of this invention is to provide a simple mechanism havingground piercing prongs that may be progressively moved along and overthe line of the suspected cable and with the device embodying certainindicating mechanism that is excited by the grounded circuit traversingthe area between the two cable grounds and with the device progressivelyregistering the magnetic influence as the device is brought closer tothe cable break, thus effectively and in a minimum of time accuratelydetermining the exact point at which the break has occurred.

The device of the present invention further contemplates an indicatorthat is solely influenced when brought into the field of energy and thatrequires no separate source of electrical energy for its operation.

Further advantages of the device will be clearly apparent during thecourse of the following description, reference being had to theaccompanying drawings wherein has been illustrated the preferred form ofthe device and wherein like characters of reference are employed todenote like parts throughout the several figures.

arra e a rms 9- he armsfiXod, n; djusted position With respect to; thecross-head 7 bybolts F xed ad ac n he o to onds. ofi herms. e depen n pes: ip nto t their ower e 'wher y tog-facilitatetheir entryv into theearth,

Fixedjointly; upon the standards 5-, adjacent the hano s; a. bo ik hou n1 a. sposedaw fl in'. th housing, 12, is a; rectifier- 133, see;particularly Figure 4;. Disposed upon the upper of the housing 12. and pojec i n e hr us or: io a-1i ob er t on, is a m r sros dt t e us s apotenomoto havingammlii i a oo to hat is dispo e d y o t us n Whorobro-sfao l tate. e ariation: isrsott :Qao. s de; i he rec ifier is conneted to one pin a l b ao sduo o 5. hile. the pp Side of the rs t fio i sanns e i to he mi ro mme er by a cn llQ 'n sg ppmiteside of-thernicroammeter. is connected to the potentiometer by a conductor 19; Thereliab e oontao f r h; n on iome er-o co nec e totho opposite probe 11by; a conductor The rectifier, ono m no o and. pote t omete e fi nyv esa l well k w s w tiom. Q QK zB e e m b dy na t e standa s h handl d, t ero se d: tho rn s. t he bes and. he h us ng may b formed of anydesirable material that is light in weight, such as aluminum. It shouldbe understood of course that the probes 11 are insulated in anydesirable manner from the arms 9 and the conductors 17 and 20 beingsuitably'insulated with respect to the structure. It is of coursedesirable that the probes 11 be formed of sufficiently hard metal aswill withstand the constant probing into the ground where theyfrequently come into contact with rocks and other subsurface obstacles.

During the constant checking by the service trucks of the power company,where it is observed that .certain street lights are either burning verydimly or entirely exfinguished, it becomes necessary toquickly determinethe exact point or points in the cable that are at fault. The operatorthen proceeds to Walk between two light standardswhere one light isburning while the other is either entirely out or burning very dimly,indicating to the operator that the fault in the cable lies between thetwo standards. He then proceeds to slowly walk between the two lightstandards, constantly probing the locator into the ground as he walksalong and noticing the action of the mjcroammeter to determine thepresence of current leaking through the ground. As he approaches thepoint 'of fault, a reading will show on the meter, such readingprogressively increasing as he approaches the point of fault. If thecurrent is of suflicient strength that the meter goes oif the scale, theoperator actuates the sensitivity control 16 of the potentiometer,bringing the meter pointer back upon. the scale. As the point where theoperator obtains the highest reading upon the meter indicates the exactspot where the cable is at fault. Thus, with a minimum of effort theexact point of breakcan be quickly determined and the ground excavatedat that point in order that the cable may be spliced or otherwiserepaired and avoids the need of several excavations along the line ofthe cable to locate the point of breakage, such as has been thecondition heretofore. The exact location results in a very considerablesaving in labor cost, since heretofore there has been no deviceavailable whereby to locate the exact point of break without firstde-energizing the cable and making direct connection of the testingdevice. Other devices are available but require direct connection tocable, are more complicated to opcrate, require more time to locatefault, and degree of accuracy is questionable. In actual practice over acon siderable length of time it has been estimated that to locate,excavate and repair a cable break requires approximately 20 minutes tohalf an hour as compared to the present practice wherein it has beencustomary to employ anywhere from two hours to a half a day. The deviceof this invention embodies no batteries or other source of power and isentirely actuated by the field of electrical energy traversing theearth, between two points of cable breakage. Obviously with only onebreak in a cable, there will be no flow of current through the earth.

It will be apparent from the foregoing that a very simple and highlyeffective means has been provided whereby to quickly and easily locate acable fault. The device is simple in construction, is strong, durable,cheap to manufacture and most effective for its purpose. The use of thisdevice to locate faults on direct burial nonmetallic sheath seriesstreet light cable will benefit the utilities in substantial savings inlabor and material costs and faster restoration of street lighting whichin turn will improve customer relations and public safety.

It is to be understood that the invention is not limited to the preciseconstruction shown but that changes are contemplated as readily fallwithin the spirit of the invention as shall be determined by the scopeof the subjoined claim.

Having described our invention, what we claim as new and desire tosecure by Letters Patent is:

A device for locating electrical cable faults in those types ofdirect-burial non-metallic sheath cables and whereby to register aminimum to maximum point of fault in the cable through the medium of afield of radi- 4 ation of electrical energy from the point of fault, thedevice embodying a frame comprising a pair of spaced apart paralleltubular standards that are fixedly connected together at their upperends by a handle device, the standards at their lower ends beingconnected together by a cross head, the underside of a cross head beinglongitudinally arcuately grooved, tubular arms adjustably engaged withinthe groove of the cross head and with the arms extending outwardly in ahorizontal plane, bolts for rigidly securing the arms in adjustedposition with respect to the cross head, each of the arms adjacent theirterminal outer ends being provided with a depending ground probe andwith the probes having a sharpened lower end, a housing supported uponthe standards, a direct-current microammeter disposed within the housingand having a variable reading dial extending above the housing forobservation by an operator holding the handle, a rectifier disposed inthe housing, electrical conductors connecting the rectifier, with oneprobe and with one side of the rnicroammeter, a potentiometer disposedwithin the housing and with the potentiometer having a variableresistance control that extends through one side of the housing, thepotentiometer being connected at one side to the microammeter throughthe medium of an electrical conductor and an electrical conductorconnecting the variable resistance control to the other of said probes,the said probes adapted to be probed into the ground along the line of asuspected cable at fault Whereby to span the area of fault and actuatethe microammeter to its point of greatest reading, the saidpotentiometer being variable to maintain a pointer of the microammeterdial within the area of calibrations formed upon the dial.

References Cited in the file of this patent UNITED STATES PATENTS2,091,521 Pattison Aug. 31, 1937 2,123,545 Pearson July 12, 19382,235,533 Roberts Mar. 18, 1941 2,378,440 Scott June 19, 1945 2,461,111Flinspach et a1. Feb. 8, 1949 2,688,116 Stahl et a1. Aug. 31, 1954FOREIGN PATENTS 855,995 France Mar. 4, 1940

